As the piezoelectric vibration device (for example crystal unit or oscillator) utilized for generation of an oscillation signal and so on, for example a tuning fork type is known (for example Patent Literature 1). A tuning fork type piezoelectric vibration device is provided with a piezoelectric blank (for example crystal blank) having a base part and a pair of arms extending parallel from the base part which utilizes vibration caused in the pair of arms by application of voltage to the pair of arms so as to generate an oscillation signal.
Patent Literature 1 discloses a piezoelectric blank in which a single groove extending along the arms is formed on an upper surface and lower surface of the arm (planes which are parallel to the direction of extension of the pair of arms and to the direction of lineup of the pair of arms). Further, Patent Literature 1, as a method of forming this one groove by etching, proposes a method of first forming two thin grooves by etching then etching away the ridge part between the two thin grooves to form a single wide groove.
Patent Literature 1 also discloses a method of not completely removing the ridge part but leaving a little. Patent Literature 1 claims that, by leaving the ridge part in the single wide groove, it is possible to increase the surface area in the single wide groove and consequently increase the area of the excitation electrode and therefore it is possible to lower the crystal impedance (CI). Further, Patent Literature 1 states to it is possible to make the deepest part of the single wide groove deeper to lower the CI while securing the rigidity of the arms by the ridge part.